Group A streptococcal infections and their sequelae have occurred with a striking increase in rate and severity in the United States during the past five years. There have been suggestions that increased virulence in strains associated with severe infections is due to the appearance of strains producing increased amounts of certain extracellular toxins. The purpose of this research is to investigate the contribution to virulence of several group A streptococcal extracellular product determinants, specifically genes encoding erythrogenic toxin A, erythrogenic toxin B (proteinase), and streptokinase, and characterize the regulatory factors which control these genes. The specific aims of this study are to: 1. Elucidate in molecular detail the mechanism of toxigenic conversion by which group A streptococci produce erythrogenic toxin A, and evaluate the presence and regulation of expression of this toxin gene in strains associated with severe diseases such as toxic shock-like syndrome, bacteremia, and rheumatic fever. 2. Perform a molecular epidemiological analysis of the erythrogenic toxin B/streptococcal proteinase precursor gene among different M serotypes and establish whether heterogeneity accounts for possible differences in proteinase activity and its role in virulence. 3. Identify and characterize regulatory factors controlling expression of extracellular product genes such as erythrogenic toxins, streptolysin O, and streptokinase, and determine whether they are coordinately regulated. The necessary tools have been developed to permit a molecular characterization of group A streptococcal virulence. This proposal has been designed to assess the role of extracellular products in strains associated with severe infections. Additionally, experiments are described to characterize the molecular mechanisms governing the regulation of these extracellular virulence factors. This information is essential for our understanding of the events that occur during the pathogenesis of streptococcal disease such as severe systemic infections, rheumatic fever, and acute glomerulonephritis.